Learning Outline

Introductory Chemistry

BIO 095

Check out Shuster's Chemistry Review for extra help with this topic.

Chemistry Essentials

Chemistry is the basis for biology

Basic structural concepts

• Atom: smallest part of a pure substance, or element, that still has the properties of that substance
  
  
• Molecule: a particle made up of one or more atoms bound together
  
  
• Element: a pure substance, made entirely of one kind of atom (all known elements are listed in the Periodic Table)
  
  
• Compound: substance made of molecules that contain more than one kind of atom

Atomic structure and function

• Many different models exist; none are perfect
  
  
  • We'll look at the Bohr model and electron cloud model first —then later structural and space-filling models
    
    
  • Bohr model (named for Niels Bohr) shows electrons orbiting the nucleus like planets orbit the sun
    
    
  • Electron cloud model (ECM) shows electrons as a cloud surrounding the nucleus

• Nucleus
  
  
  • Protons have positive (+) charge; number of protons is "atomic number" and signifies kind of atom (which element)
    
    
  • Neutrons have no charge; optional and variable in number (isotopes)
    
    
• Electrons
  
  
  • Electrons have a negative (-) charge and do not affect the type of element
    
    
  • Electrons may be present in regions called energy levels
    
    
    • The further from the nucleus, the more energy is needed by the electron to stay there --so the higher energy levels are farther from the nucleus
      
      
    • The lowest (first) energy level can contain up to two electrons
      
      
      • The next few can hold up to eight electrons each (the "octet rule")
        
        
    • Energy levels fill from the inside out
      

Behavior of atoms: chemical bonds

• Atoms want to be "happy"—meaning having a full outer energy level
  
  
• One path to happiness: ionic bonds
  
  
  • Occurs when an atom gives one or two electrons to another atom, giving both "full" outer energy levels
    
    
  • Ion: charged particle (atom or group of atoms)
    
    
  • Ions "stick" together because opposite charges attract —forming a bond
    
    
  • Electrolyte: molecule that dissolves in water to form ions
    
    
    • Sometimes the individual, dissolved ions are also called electrolytes
      
      
• Another path to happiness: covalent bonds
  
  
  • Outer level is "valence" level (from Latin word for outer garment)
    
    
  • Occurs when atoms share valence electrons (co-valent, get it?)
    
    
  • Sharing may not be equal
    
    
    • Polar molecules occur when sharing is NOT equal
      
      
      • Polar molecules are hydrophilic, or "get along with water"
        
        
      • Ions also "get along with water"
        
        
    • Nonpolar molecules occur when sharing IS equal
      
      
      • Nonpolar molecules are often hydrophobic, "don't get along with water"

Other attractions (sometimes also referred to as "bonds" or "weak attractions")

• Hydrogen bonds (formed when polar molecules stick together)
  
  
• Other weak attractions from temporary shifts in charge within molecules
  

Water

• Water is cohesive—hydrogen bonds make it "sticky"
  
  
• May be represented H₂O or H-O-H or HOH
  
  
• Solvent: something in which other molecules (solutes) are dissolved
  
  
• Solution: mixture of solutes dissolved in a fluid solvent
  

pH: acids, bases, and buffers

• Water molecules may dissociate into H⁺ and OH^-
  
  
  • H⁺ is the hydrogen ion
    
    
  • OH^- is the hydroxide ion
    
    
• Solutions with equal proportion of H⁺ and OH^- are "neutral"
  
  
• Acids: solutions with higher proportion of H⁺
  
  
• Bases: solutions with a lower proportion of H⁺ (alkaline solutions)
  
  
• Can be expressed as "power of Hydrogen" or pH
  
  
  • pH scale is an inverse (base 10) logarithm of relative H⁺ concentration
    
    
  • 7 = neutral
    
    
  • acid = anything lower than 7
    
    
  • base = anything higher than 7
    
    
  • human blood plasma = pH 7.35-7.45
    
    
• Buffer: system of molecules that absorb or release H⁺ —maintaining a relatively stable pH